1. Field of the Invention
The present invention relates to a pump provided with a housing and a rotor that rotates within the housing, the pump drawing fluid into the housing and forcing the drawn fluid to the exterior of the housing. The present invention also relates to an ink jet printer mounting this pump.
2. Description of the Related Art
Rotary pumps are known to the art. One example of a rotary pump is set forth in Principles of New Machinery, 1997, Tenth Edition, p. 203 (27.13 Cary's rotary pump, part 1) “Kikai no so Fukkan Iinkai Hensha, Rikogakusha”. This pump is termed a Cary's rotary pump.
As shown in FIG. 9, a Cary's rotary pump 70 is provided with a housing 73, a rotor 74, a pair of blades (separating members) 76a and 76b and a compressed spring 75. An inlet port 71 and an outlet port 72 are formed in the housing 73. The rotor 74 is cylindrical, and has a groove 78 therein extending across its diameter. The rotor 74 rotates while making contact with a portion of an inner face of the housing 73 between the inlet port 71 and the outlet port 72. The pair of blades (the separating members) 76a and 76b are housed in the groove 78. The compressed spring 75 is housed between the pair of blades (the separating members) 76a and 76b. The compressed spring 75 presses the pair of blades (the separating members) 76a and 76b against the inner face of the housing 73.
When the rotor 74 rotates, the pair of blades 76a and 76b rotates integrally with the rotor 74 while making contact with the inner face of the housing 73. Centrifugal force operating on the pair of blades 76a and 76b increases the force pressing the pair of blades 76a and 76b against the inner face of the housing 73.
The pair of blades 76a and 76b and the rotor 74 separate a cavity within the housing 73 into three divided spaces. That is, the cavity within the housing 73 is separated into: a divided space 77a linked with the inlet port 71, a divided space 77b linked with neither the inlet port 71 nor the outlet port 72, and a divided space 77c linked with the outlet port 72.
When the pair of blades 76a and 76b are rotating integrally with the rotor 74, this rotation occurring in a clockwise direction, and while the pair of blades 76a and 76b are making contact with the inner face of the housing 73, the volume of the divided space 77a linked with the inlet port 71 increases, and the volume of the divided space 77c linked with the outlet port 72 decreases. The increase in volume of the divided space 77a linked with the inlet port 71 draws fluid such as water, air, or the like, into the housing 73 from the inlet port 71. The decrease in volume of the divided space 77c linked with the outlet port 72 elevates the pressure of the fluid drawn into the housing 73, and this pressurized fluid is discharged to the exterior of the housing 73 from the outlet port 72.
In the case of, for example, an ink jet printer, ink must be supplied to an ink jet head from an ink cartridge. During ordinary printing, pressure decreases in an ink passage within the ink jet head when ink is discharged from the ink jet head, and ink is consequently drawn into the ink jet head. There is no need to force ink towards the ink jet head during ordinary printing.
However, air bubbles or the like may be entrapped in the ink passage within the ink jet head when, for example, the ink cartridge has been changed. In this case, it is necessary to discharge the entrapped air bubbles or the like by forcing ink towards the ink jet head (this process is termed purging). A pump must be provided between the ink cartridge and the ink jet head for performing the purging operation.
The pump for the ink jet printer is required to force ink out through the outlet port when the pump is rotating, and required to allow ink to flow from the inlet port to the outlet port when the pump is not rotating.
However, in the conventional rotary pump 70 shown in FIG. 9, the inlet port 71 and the outlet port 72 is separated by the rotor 74 and the pair of blades 76a and 76b when the rotary pump 70 is not moving. Consequently, fluid cannot flow from the inlet port 71 to the outlet port 72 when the rotary pump 70 is not moving.
It is possible to maintain a passage between the inlet port 71 and the outlet port 72 by forming a cut-away portion in an outer peripheral surface of the rotor 74 of the rotary pump 70 shown in FIG. 9. This allows a pump 70 to be realized in which fluid flows from a supply source to a supply destination even when the pump 70 is not moving.
This type of rotary pump is disclosed in Laid-Open Japanese Patent Application Publications 2004-268272 and 2004-270455. The pump disclosed in these publications comprises the rotor having the cut-away portion in its outer peripheral surface, and the passage from the inlet port to the outlet port is maintained when the pump is halted.